Magnetic chucks



Nov. 18, 1958 E. H. BRANDENBURG Y 2,861,224

MAGNETIC CHUCKS Filed Oct. 17, 1952 s Sheets-Sheet 1 Fig.

IN V EN TOR.

Nov. 18, 1958 E. H. BRANDENBURG 2,361,224

MAGNETIC CHUCKS Filed-Oct. 17, 1952 s Sheets-Sheet 2 BY%A7%[7 A Nov. 18, 195 8 E. H. BRANDENBURG 2,86

MAGNETIC CHUCKS Filed 001:. 1'7, 1952 3 Sheets-Sheet 5 BY KW! United States Patent MAGNETIC CHUCKS Edwin H. Brandenburg, Lakewood, Ohio Application October 17, 1952, Serial No. 315,386

1 Claim. (Cl. 317-163) This invention relates to electromagnets of the lifting or holding class.

While the invention may be applied to various kinds or types of lifting magnets and holding magnets, and used in various arts, it is particularly applicable to holding work pieces to be worked by a machine tool; and in order to make a concrete disclosure of the invention herein, as required by law, I have chosen to illustrate and describe it as embodied in a so-called magnetic chuck for holding work pieces in a lathe.

Magnetic chucks are known having a work contacting surface upon which ferrous work pieces may be laid and magnetically held against slipping (when subjected to the force or torque of a tool working the piece), by magnetic flux produced by a winding and flowing from one end of the winding core through the work contacting surface into the work piece, and out of the work piece back into the work contacting surface and thence by a return magnetic path of the structure to the other end of the winding core.

The work contacting surface of such known chucks, is thus in two parts on two pole pieces of a magnetic circuit, separated from each other magnetically, and functioning as two magnetic pole faces of opposite polarity namely: a magnetic pole face of one polarity (say north) where the flux leaves the surface and enters the work piece, and a pole face of south polarity where the flux reenters the surface.

It has been proposed to have the two pole faces of such prior chucks in a common plane, and to separate them by non-magnetic spacing material flush with the said plane, so that the whole work contacting surface is smooth and planar and the work piece can be freely moved on the surface to position it or to center it on a pilot; before the current energizing the winding is turned on.

It has also been proposed to shape the opposite-polarity pole pieces so that the space between them and the spacing material therein is of suitable uniform width, say A", and follows a zig-zag path or pattern. By this means if a work piece covers enough of the said planar surface, it may overlap the said space at several points and will thus lie upon a plurality of north and south pole face portions and accordingly be more firmly gripped upon the surface.

This principle of design has been proposed for rotary magnetic chucks for lathes. They are generally circular around the rotational axis; and the flux originates in the central portion of one of the pole pieces, whereby the flux may be produced by a single winding around a coaxial core, with advantages of simplicity and economy in manufacture.

However, in such prior chucks, in order to provide the aforesaid plurality of alternating north and south pole face portions on a considerable area of the planar work engaging surface, it has been necessary to make the pole pieces of such shape that the said space between them follows a zig-zag path having in general the contours of a star; that is to say, there must be portions of an inner pole piece extending outwardly radially, with notches or valleys between them, and corresponding portions of 2,861,224 Patented Nov. 18,1958

an outer pole piece extending radially inwardly into the notches or valleys.

For reasons of desired high magnetic permeability, the pole pieces must be machined to shape from steel blanks, and to give them such irregular form is a costly manufacturing operation.

This objection to prior magnetic chucks, would be overcome if the pole pieces or pole face portions could be annular or generally circular in shape because then they could be cut to that shape by a cheap simple lathe operation.

It is therefore the primary object of the present invention, to provide an improved chuck of the class referred to having a magnetic work-gripping planar surface, divided up into a plurality of magnetic pole face portions, separated from each other by non-magnetic spaces, and the pole face portions and the spaces between them being annular or generally circular in form, and the pole face portions all being energized by flux, from a single coaxial winding.

Another object is to provide a magnetic chuck as referred to above in which some of the annular pole pieces and spacers constitute a unitary assembly, detachably mounted in the chuck.

With these and other objects in view the invention comprises, generally, a magnetic chuck adapted to be mounted in a lathe to be rotatably driven thereby and having a planar surface for gripping work magnetically, the gripping surface divided up into a plurality of generally circular or annular concentric surface portions by annular non-magnetic spacers; and all of the surface portions energized with magnetic flux from a single coaxial electric winding.

The actual invention is that set forth in the appended 7 claim.

The invention is fully disclosed in the following description taken in connection with the accompanying drawing in which:

Fig, 1 is a view of an embodiment of the invention, partly in elevation and partly in longitudinal section;

Fig. 2 is a top plan view of the embodiment of Fig. 1;

Figs. 3 and 5 are views similar to Fig. 1 but with parts broken away, illustrating a modification; and

Figs. 4 and 6 are top plan views of the embodiments of Figs. 3 and 5, respectively.

Referring to the drawing, Figs. 1 and 2, there is shown generally at A, parts of a magnetic circuit generally of cup form, comprising a tubular side wall or cup skirt 1 of steel, threaded at its lower end as at 2 upon a steel cup bottom 3; the latter having an integral shank 4, internally bored and threaded as at 5, coaxially with the Wall 1, for screwing it upon the hollow spindle of a lathe (not shown), by which the chuck is mounted on the lathe, to be rotated thereby.

A cylindrical core 6, integral withthe bottom 3 extends coaxially within the wall 1.

The upper end portion of the core 6 (as viewed in Fig. 1) is of reduced cross-sectional area for a portion of its length as shown at 7.

A steel sleeve 8 is telescoped over the core 6 and is press fitted thereon.

A winding 9 surrounds the sleeve 8, disposed in the space between the sleeve 8 and side wall or cup skirt 1.

A diagonal bore 10, through the bottom 3, communicates with the winding 9 and with the threaded bore 5 by which terminal wires from the winding 9 may be led from the winding through the hollow lathe spindle to an exterior point therebeyond and connected to a rotary contact device of well-known type to energize the winding.

As shown at 11, the sleeve 8 is interiorly cylindrical from end to end, and provides a tubular or annular space between the reduced diameter portion 7 of the core 6 and the inner wall of the sleeve 8, and this space is'filled with a hard-setting, non-magnetic metal alloy, having low melting temperature.

The outer cylindrical surface of the steel sleeve 8 at its upper end, is cut down in diameter for a portion of its length, providing a portion 12 of reduced cross sectional area, and providing an outer cylindrical surface 13 and a shoulder 14-. A metal non-magnetic ring 19 is pressfitted over the surface 13.

At some distance below the shoulder 14, the outer surface of the sleeve 8 is cut down to a shallow depth to provide a cylindrical surface 15 and a shallow shoulder 16. The outer surface of the ring 19 is formed to be a continuation of the cylindrical surface 15.

At the upper end of the wall 1, its inner surface is cut back on the inside for a portion of its length, providing a cylindrical surface 17 and a shoulder 18.

An assembly of two rings and 21 is made, the rings being internally and externally coaxially cylindrical, and being press-fitted upon each other.

The outer ring 21 is sized to be press fitted within the surface 17 of the wall 1, and to bottom on the shoulder 18, whereby a unitary assembly of the rings 20 and '21 and side wall 1 is made, designated at B.

The ring 20 is sized to slidingly fit the said cylindrical surface 15.

When the side wall 1 is screwed onto the bottom 3, at 2, the ring 2th propelled axially thereby telescopes inwardly with a sliding fit over the surface 15 and bottoms on the shoulder 16.

The rings 19 and 21 are of brass or other non-magnetic material, and the ring 20 is of steel, and both are above the winding 9.

The relative radial and axial dimensions of the rings 19, 20 and 21 may be varied, actual dimensions not being critical, and preferred proportions therefor are shown, in the drawing.

After the assembly B is assembled in the structure, the top surface of the device (as viewed in Fig. 1) is machined ofi in a plane indicated at 22 at right angles to the axis of the threaded bore 5.

All of the rings 19, 20 and 21 being seated upon shoulders as described, there is no liability that they will be displaced, inwardly, by accidental blows on the outer planar surface 22.

The structure described also provides for giving access to the winding 9, for its removal, for replacement or repairs by unscrewing the skirt wall 1, and removing it.

To insure rotation of the rings 20-21 with the side wall 1 when screwing and unscrewing it, a plurality of screws 23'23, preferably three or four, are projected through bores 2424 in the wall, the bodies of the screws fitting the bores, and their inner ends threaded into the ring 21. If preferred, the screws may be continued into the ring 20.

From the above description it will be seen that the planar gripping surface .22 is composed of a circular central surface portion 25 at the end of the core portion 7; an annular surface portion 26 at the end of the sleeve 8; an annular surface portion 27 at the end of the ring 20; and an annular surface portion 28 at the end'of the wall 1;the said surface portions being separated by annular non-magnetic spacers 11,19 and 21.

In operation of the chuck, magnetic flux produced by the winding 9 when energized, flows upwardly in the core 6 and sleeve 8 and emerges from the surface portions 25 and 26.

Some of the flux in the sleeve 8 flows into the ring 2! where the sleeve and ring overlap axially at the surface 15, and emerges from the surface portion 27 of the ring.

All of the flux emerging from the said surface portions 25, 26 and 27 returns to the core 6 and sleeve 8, by entering the upper end of the wall 1 at its surface portion 28.

Thus the flux originating in the core 6 within the winding is not distributed at low density over the whole area ofthe surface 22, but is concentrated intheannular surface portions of reduced area.

A work piece placed on the planar surface 22 will be gripped by the flux emerging from one or more of the said surface portions 25, 26 and 27 which it overlaps; and if the piece overlaps the surface portion 28 it will also be gripped by the flux entering it; and the flux being thus concentrated in surface portions of reduced area, strong gripping action is produced.

The torque exerted on a work piece, gripped on the surface 22 and rotating with the chuck, which torque is developed by a tool cutting the work piece, increases with the radial distance of the cut from the axis of the chuck.

It is therefore desirable for the opposition to this torque produced by the gripping action, to also be greater at greater radial distances from the axis.

This result could if desired be obtained by. making the gripping action itself progressively greater at progressively greater radial distances from the center, for example by proportioning the areas of the annular surface portions and the flux in them to give greater concentration and flux density therein; but if this were done, the said opposing torque, which is the product of the gripping action and the radial distance, would be greater than necessary, and some of the advantages of the invention as to simplicity would thereby be lost because more flux than necessary would have to be produced, requiring a larger winding and magnetic circuit, and resulting generally in an oversized device.

Accordingly, low manufacturing cost of the chuck of the invention is attained by making the gripping action itself, at the several surface portions 25, 26, 27 and 28, in general the same at their increasing radial distances, or, if it varies due to irregularities in manufacture, etc., by causing it to increase rather than decrease, explained as follows.

The flux in the axial core portion 7 is of high density due to its reduced cross sectional area, and exerts a certain gripping action at its surface portion 25, with the minimum of flux.

The flux in the sleeve 8 is partly diverted into the ring 20 at the overlapping surface 15 so'that only a part of it goes on to the sleeve portion 12; and that .part is concentrated due to the reduction of the cross sectional area; but the density of the flux is not high because the total flux is small; and although the area of the annular surface portion 26 is greater than that of the surface portion 25, the reduced density makes the gripping action about the same as that at 25.

The flux diverted into the ring 20 at the cylindrical surface 15 is dispersed in the ring and is at low density therein, but the annular surface portion 27 at which the dispersed flux'emerges is of large radial extent and diameter and therefore of large area, which compensates for the low density and makes the gripping action again about the same as that at 25.

The fiux entering the surface portion 28, is the sum of that emerging from the other surface portions, but the area of the surface portion 28 is largest of all, being on such a large diameter and of relatively great radial thickness; so that although the flux is of great amount, it is at low density, and the large area at low density again makes its gripping action about the same as that at 25.

It is believed that it will now be apparent to those skilled in the art in view of the foregoing analysis of .Figs. 1 and .2 giving the relative proportions of the cross sectional areas, of the parts 7, 12 and 20 and 1 and of the areas of the surface portions 25, 26, 27 and 28, that if it should be desired to make the gripping action at the surface portions 25, 26, 27 and 28, successively greater instead of approximately the same as described, that this can be done by making'corresponding changes in said proportions, to give progressively more concentration of flux in the surface portions 26; 27 and 28? by making, them of smaller area.

As will be seen the particular embodiment of the invention described comprises four gripping surface. 'portions, 25, 26, 27 and 28, in the work gripping plane 22, all completely circular or annular, that is,not interrupted or discontinuous circumferentially, and all energized with flux from a single winding.

As a statement of the structural and magnetic principles of the device, as thus far described it may be said, that the flux originates in a core within the winding; and that, beyond the ends of the winding, the core ,comprises annular or circular branches; and, that the work gripping surface comprises magnetically separated annular or circular surface portions, each of the surface portions energized by one of the branches.

The particular embodiment of the invention, illustrated and described in Figs. 1 and 2, comprises three magnetic branches 7, 12, 20 from the upper end of the core (as viewed) energizing three surface portions 25, 26 and 27; and a single branch 1, from the lower end of the core energizing a single surface portion 28; and the surface portions 25, 26, 27 may be considered as of positive polarity and the surface portion 28 as negative polarity.

However, the aforesaid principles of the device may be embodied in other arrangements of core branches and surface portions and polarities thereof, two of which are shown in Figs. 3-4 and Figs. 5-6, respectively, as illustrative of the scope of the claimed invention. 1

A general comparison of the three forms will first be given as follows:

In Figs. 1 and 2, described above, the core has three branches 7, 12 and 20 at the upper end energizing surface portions 25, 26 and 27, at, say, positive polarity and one branch, 1, at the other end energizing surface portion 28 at negative polarity.

In Figs. 3 and 4, as will be described, there is a single branch from the upper end of the core energizing a single annular surface portion of positive polarity, and three branches from the lower end of the core, energizing three annular surface portions at negative polarity.

In Figs. 5 and 6, as will be described, there are two branches from the upper end of the core energizing two annular surface portions of positive polarity and two branches from the lower end of the core, energizing two surface portions, at negative polarity.

The form of Figs. 3 and 4 is similar in some respects to that of Figs. 1 and 2 and a brief description will suffice.

A core 29 extends from the cup bottom 3, and is cut back at the upper end portions to provide a portion 30 of reduced cross section, and a cylindrical surface 31 and a shoulder 32.

The annular side wall or cup skirt 33, threaded on the bottom 3 at 2, is cut back on its inside to provide a cylindrical surface 34 and a shoulder 35, leaving an annular portion 36 of reduced cross section.

A steel sleeve 37 is telescoped and press-fitted into the side wall 33.

A filling 38 of non-magnetic metal alloy, as referred to above, fills the annular space between the sleeve 37 and the surface 34.

Outer rings 39 and 40 of brass or other non-magnetic material and an intermediate ring 41 of steel, externally and internally cylindrical, are press-fitted together in a ring assembly; and the ring assembly is press-fitted into the sleeve 37 making a unitary assembly with the sleeve 37 and wall 33, designated at C.

The ring 41 has a radially, outwardly, downwardly, sloping inner end 42 extending under the ring 39, upon which the ring 39 bottoms; and has a cylindrical surface 43 in continuation of the outer cylindrical surface of the ring 39 and in contact with the sleeve 37.

The ring 40 has a sliding fit around the surface 31; whereby the rings can be put into the positions illustrated by screwing the unitary assembly C onto the bottom at 2,

the ring 40 concurrently slidingly telescoping overthesurface 31 and bottoming on the shoulder 32.

A winding 44 surrounds the core 29 in the space between the core and the sleeve 37, and is made accessible upon screwing the unitary assembly C outwardly and removing it.

The upper end of the assembly is machined off to a work gripping plane 45; and the structure then provides work gripping surface portions as follows; a circular or annular surface portion 46 on the central core portion 30; an annular surface portion 47 on the ring 41; an annular surface portion 48 on the sleeve 37; and an annular surface portion 49 on the side wall 33.

Flux, considered as flowing upwardly in the core 29, flows out at the surface portion 46 and into a work piece on the work gripping surface 45, and thence into the surface portion 47 of ring 41 and through the ring and through the. contacting surface 43 and into the sleeve 37; and from the work piece into the surface portions 48 and 49 and into the sleeve 37 and wall 33 respectively,

and thence back to the other end of the core; thus ener-- gizing onesurface portion 46 at positive polarity, and three surface portions 47, 48 and 49 at negative polarity.

In Figs. 5-6, a core 50 extends from the cup bottom 3, and is cut back at the upper end to provide a portion 51 of reduced cross section, and a cylindrical surface 52 and a shoulder 53.

A steelsleeve 54 is press-fitted over the core 50, leaving an annular space between it and the cylindrical surface 52 which is filled with non-magnetic metal alloy as hereinbefore described.

The sleeve 54 is cut back on the outside at its upper end portion to make it of reduced cross-section as at 56 and to provide a cylindrical surface 57 and a shoulder 58.

The outer wall or cut skirt 59 is threaded on the bottom 3 at 2, and at its upper end is cut back on its inner side to provide an upper end portion of reduced cross-section at 60, and a cylindrical surface 61, and a shoulder 62.

Rings 636465 internally and externally cylindrical, are made and press-fitted together, the rings 63 and being of brass or other non-magnetic material, and the intermediate ring 64 of steel; and the outer ring 65 is press-fitted within the surface 61 to make a unitary assembly indicated at D, comprising rings 63-64--65 and the side wall 59.

The ring 64 has a radially outwardly downwardly sloping inner end 66, and a radially outwardly cylindrical surface 67 in continuation of the press-fitted cylindrical surfaces of the rings 64 and 65.

The ring 63 is sized to have a sliding fit within the surface 57 of the sleeve 54, whereby when the assembly D is screwed onto the bottom at 2, the ring 63 will be tele' scoped into the position illustrated and bottomed on the shoulder 58.

A winding 68 surrounds the sleeve 54 in the space between ,the sleeve and the side wall 59, and is made accessible by unscrewing the assembly D and removing it.

The upper end of the whole assembly is machined off to a work gripping plane 69; and the structure then provides work gripping surface portions as follows; a circular or annular surface portion 70 on the central core portion 51; an annular surface portion 71 on the end of the sleeve 54; an annular surface portion 72 on the ring 64; and an annular surface portion 73 on the end of the wall 59.

Flux considered as flowing upwardly in the core 50 and sleeve 54, flows out at the surface portions 70 and 71, into a work piece on the work gripping surface 69; and from the work piece into the surface portion 72 of the ring 64 and through the ring and through the surface 67 to the wall 59; and from the work piece into the surface portion 73 to the wall 59; thus energizing two surface portions 70 and 71 at positive polarity and two surface portions 72 and 73 at negative polarity.

The screws 23--23 of Figs. 1 and 2 have been omitted from Figs. 3-4 and Figs. -6 for simplification, but it is believed that it will be clear how they may be added.

It has been found that it is not necessary as in prior structures, to have the adjacent surface portions of alternate polarity in order that the flux will always enter the work piece at one polarity and leave at the other polarity; but has been found that the same gripping effect will be obtained, when, as here the successive surface portions across the gripping surface are annular, and are-of like polarity.

In Figs. 1 and '2 flux enters the work piece at three adjacent surface portions of positive polarity and leaves it at one surface portion of negative polarity. In Figs. 3 and 4 it enters at one surface portion of positive polarity and leaves out three adjacent surface portions of negative polarity; and in Figs. 5 and 6 it enters at two adjacent surface portionsof positive polarity and leaves at two adjacent surface portions of negative polarity.

I claim:

A work holding electromagnetic device comprising a generally cup-form magnet having a cup bottom, and a cup skirt, annular in cross section, extending from the periphery of the cup bottom, and a core extending from the middle of the cup bottom, substantially coaxial with the skirt; and a shank extending from the cup bottom oppositely to the skirt and core; the shank being provided with means for attaching it to a rotary element of a machine for rotating the'cup bottom, skirt and core around a rotational axis; the core comprising an inner generally cylindrical body, and at its outer end being of reduced diameter over a portion of its length; a steel sleeve having a substantially uniform inside diameter telescoped over the core body and its inside surface spaced radially from the reduced diameter portion of the core, and the space being filled With non-magnetic solid material; a

- "windin'g'insi'de of the skirt, surrounding the sleeve and the core therewithin, the top of the winding being inwardly of the outer ends of the core and skirt; the outside side surface -"of the sleeve at its outer end and over a portion of its length being of reduced diameter; a steel-ring above the winding having its inside annular surface telescoped over and fitting upon an outside surface portion of the sleeve inwardly of the reduced diameter sleeve portion,

and providing an annular space between the ring and the reduced diameter portion of the sleeve, the space being filled with non-magnetic solid material; a ring of non magnetic material above the winding and fitting between the outside annular surface of the steel ring and the inside surface of the skirt; the axially outermost portions of the core, sleeve, steel ring and skirt and of the non-magnet material all being in a'common plane at right angles to the said rotational axis; whereby work engaging annular surfaces sp'acedapart radially are provided on the core,

sleeve, steel ring and skirt; and whereby flux may be produced by the winding in the core and sleeve, and some "of the flux in the sleeve, may flow into the steel ring and all of it may -fioW outwardly through the said work engaging surfaces on the core, sleeve and steel ring, energizing these surfaces at one polarity, and all of it may flow back into the skirt through the work engaging surface thereon, energizing it at the opposite polarity.

References Cited in the file of this patent UNITED STATES PATENTS 

